Video playback devices including DVD (Digital Versatile Disc) players and BD (Blu-ray Disc) players are developed in recent years. Such a player is capable of reading video stream data from a recording medium such as a DVD or a BD and playing back a moving image. While playing back the moving image, the player may also execute an application recorded on the recording medium, and display an image related to the application separately from the moving image. Examples of this include displaying, beside the moving image, a menu GUI (Graphical User Interface) relating to the moving image, and displaying subtitles.
Here, the player combines (overlays) the moving image and the image which is subjected to a display control by the application to generate image data, and displays the generated image data on a display. Data to be combined is sequentially read from the recording medium and written to a corresponding area on a memory of the player. The player reads image data from the memory, combines the image data, and outputs a resulting composite image. The corresponding area on the memory of the player is any of a video plane for storing image data of the moving image, an IG (Interactive Graphics) plane for storing image data of a GUI menu to be displayed together with the moving image, and the like. To combine images, the player needs to access each plane.
The player needs to access each plane at high speed when producing a composite image. To play back video without a delay, it is important to effectively use a memory bus upon such access.
Patent document 1 describes a technique relating to memory writing. According to this technique, when a GUI object needs to be drawn again, unnecessary writing to a memory is suppressed by a checking means for specifying an area that needs to be repaired and a generation means for determining an object that needs to be drawn again. A memory bus bandwidth can be effectively used as a result of suppressing unnecessary writing in this way.
Patent document 1: Japanese Patent Application Publication No. 2004-102343